A liquid crystal display device has been widely used in displays of personal computers, televisions, and the like. This device employs optical anisotropy, dielectric anisotropy, and the like of a liquid crystal compound. The following operating modes have been known as operating modes of the liquid crystal display device: a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode, a polymer sustained alignment (PSA), and the like.
In particular, the IPS mode, the FFS mode, and the VA mode are known to be able to widen a narrow viewing angle, which is a drawback of the operating modes such as the TN mode and the STN mode. In a liquid crystal display device having this type of mode, a liquid crystal composition having negative dielectric anisotropy is mainly used. In order to further improve the characteristics of the liquid crystal display device, it is preferred that a liquid crystal compound contained in the composition have the following physical properties (1) to (8).                (1) High stability to heat, light, and the like        (2) High clearing point        (3) Low minimum temperature of liquid crystal phase        (4) Small viscosity (η)        (5) Suitable optical anisotropy (Δn)        (6) Large negative dielectric anisotropy (Δ∈)        (7) Suitable elastic constant (K33: bend elastic constant)        (8) Excellent compatibility with other liquid crystal compounds        
The effects of the physical properties of the liquid crystal compound on the characteristics of the device are as described below. The compound having high stability to heat, light, and the like as in (1) increases the voltage holding ratio of the device. With this, the service life of the device is prolonged. The compound having a high clearing point as in (2) enlarges the temperature range in which the device can be used. The compound having a low minimum temperature of a liquid crystal phase, such as a nematic phase and a smectic phase, particularly having a low minimum temperature of a nematic phase as in (3) also enlarges the temperature range in which the device can be used. The compound having a small viscosity as in (4) shortens the response time of the device.
The compound having suitable optical anisotropy as in (5) improves the contrast of the device. Depending on the design of the device, a compound having large optical anisotropy or small optical anisotropy, that is, suitable optical anisotropy is required. In the case of shortening the response time by reducing a cell gap of the device, a compound having large optical anisotropy is suitable. The compound having large negative dielectric anisotropy as in (6) decreases the threshold voltage of the device. With this, the power consumption of the device is decreased.
Regarding (7), the compound having a large elastic constant shortens the response time of the device. The compound having a small elastic constant decreases the threshold voltage of the device. Thus, a suitable elastic constant is required depending on the characteristics intended to be improved. A compound having excellent compatibility with other liquid crystal compounds as in (8) is preferred. This is because liquid crystal compounds having different physical properties are mixed to regulate the physical properties of the composition.
Hitherto, as a component of the liquid crystal composition having negative dielectric anisotropy (λ∈), a large number of liquid crystal compounds in which hydrogen at a lateral position of a benzene ring is substituted by fluorine have been investigated (Patent Literature 1 and Patent Literature 2). For example, a compound (a) has been reported. However, although the compound (a) has negative dielectric anisotropy (Δ∈), the value thereof is not necessarily large in some cases, and hence the value is not sufficient for decreasing the drive voltage of a liquid crystal display device in a VA mode, an IPS mode, and the like in some cases.

Under such circumstances, there is a demand for the development of a compound having excellent physical properties and suitable balance regarding the above-mentioned physical properties (1) to (8). In particular, there is a demand for a compound having large negative dielectric anisotropy.